Systems for imaging structures of a subject and related methods

ABSTRACT

Systems for imaging structures of a subject are provided. The subject has an optical axis, a pupil, and a nodal point. The system includes an image capture device; a first structure including a mount for the subject to be imaged by the image capture device, the first structure providing at least two rotational degrees of freedom; a second structure including a mount for the image capture device, the second structure providing at least two translational degrees of freedom; and a means for aligning the image capture device in relation to the optical axis, the pupil, and the nodal point of the subject.

CLAIM OF PRIORITY

The present application claims priority from U.S. ProvisionalApplication No. 61/174,589, filed May 1, 2009, the disclosure of whichis hereby incorporated herein by reference as if set forth in itsentirety.

FIELD

The present invention relates generally to imaging systems and, moreparticularly, to high-throughput imaging systems for fine alignment ofan eye of a subject for ophthalmic imaging applications.

BACKGROUND

Preclinical imaging of small animals, for example, rodents, is importantin drug development and research exploring genetics and the earlydiagnosis of diseases. Several neurological conditions have amanifestation in retinal tissue, and can present as lesions in theretinal layers at very early disease stages. Thus, there is, muchutility in the ability to diagnose disease by identifying structuralchanges in the retinal layers, starting with piscine (fish) and murine(rodent) models.

Precise alignment of the rodent eye to an optical system, for example,optical coherence tomography (OCT) imaging systems has been a challengefor researchers. Rodents have been historically hard to image becauseof, for example, the small eye size, poor imaging properties of the eye,and lack of stage that enables the precise alignment of a rodent eye tothe optical beam of a fundus camera or clinical OCT scanner. Thedevelopment of a hand-held OCT probe, while enabling breakthroughs notpreviously possible, has not made the task much easier by itself, due tothe lack of fine control over the angles between the optical axis of theOCT probe and the axis of the rodent eye. The mouse eye has anapproximate diameter of 3.3 mm, while the rat eye diameter is around 6.4mm, and thus, manipulations on a micro level are typically necessary toenable the acquisition of good quality images of the rodent retina. Theball lens phenotype of the rodent eye compared to the human eyetypically requires very different optics to capture images of the layersin as fine detail. The design of the specific optics is discussed incommonly assigned United States Patent Publication No. 2009/0268161,published on Oct. 29, 2009, entitled OPTICAL COHERENCE TOMOGRAPHY (OCT)IMAGING SYSTEMS HAVING ADAPTABLE LENS SYSTEMS AND RELATED METHODS ANDCOMPUTER PROGRAM PRODUCTS.

SUMMARY

Some embodiments discussed herein provide systems for imaging structuresof a subject. The subject has an optical axis, a pupil, and a nodalpoint. The system includes an image capture device; a first structureincluding a mount for the subject to be imaged by the image capturedevice, the first structure providing at least two rotational degrees offreedom; a second structure including a mount for the image capturedevice, the second structure providing at least two translationaldegrees of freedom; and a means for aligning the image capture device inrelation to the optical axis, the pupil, and the nodal point of thesubject.

In further embodiments, axes of the at least two rotational degrees offreedom of the first structure may intersect. An optical axis of theimage capture device mounted on the second structure may be aligned tointersect the intersecting axes of the at least two rotational degreesof freedom of first structure. The mount for the subject in the firststructure may be configured such that the optical axis of the subject isaligned to within about 5.0 degrees of the optical axis of the imagecapture device mounted to the second structure when the subject ispositioned in the mount of the first structure. The subject may bealigned to within from about 0.0 degrees to about and 45.0 degrees.

In still further embodiments, the mount of the first structure may beconfigured such that the axes of the two rotational degrees of freedomintersect at the nodal point of the subject when the subject ispositioned in the mount of the first structure. The nodal point of thesubject may be approximated by a pupil of the subject.

In some embodiments, an optical axis of the image capture device of thesecond structure may be rotated about the nodal point of the subject ofthe first structure such that an angle between the optical axis of theimage capture device and the optical axis of the subject sweeps througha cone of at least about 15.0 degrees in at least two non-co-planardirections.

In further embodiments, an optical axis of the image capture device ofthe second structure may be rotated about the nodal point of the subjectof the first structure such that an angle between the optical axis ofthe image capture device and the optical axis of the subject sweepsthrough a cone of at least about 30.0 degrees in at least twonon-co-planar directions.

In still further embodiments, the at least two rotational degrees offreedom of the first structure may include a rotation about a first axissubstantially parallel to a first axis of symmetry of the subject and arotation about an orthogonal second axis substantially parallel to asecond axis of symmetry of the subject.

In some embodiments, the subject may be a small animal; and the firstaxis of symmetry of the small animal may be an axis of the body thatseparates a right side of the small animal from a left side of the smallanimal and a right eye of the small animal from a left eye of the smallanimal. The second axis of symmetry of the small animal may be an axisorthogonal to the axis of the body located such that the pupil of atleast one eye of the small animal lies in the plane. The small animalmay be one of a rodent, a rabbit, a monkey, a dog, a sheep, a cow, afish, a spider, a turtle, a snake, a frog, an octopus, a chicken, or abird of prey.

In further embodiments, the small animal may be one of a mammal, a fish,a bird, a reptile, an amphibian, an insect, or a mollusk. In certainembodiments, the subject may be an animal, for example, a vertebrate oran invertebrate animal.

In still further embodiments, the means for aligning may be identifyingan intersection of two axes of rotation of the subject mount; aligningthe image capture device such that an optical axis of the image capturedevice intersects the axes of rotation of the subject mount; positioningthe subject such that the nodal point of the subject eye is located atthe intersection of these two axes of rotation and an imaging axis ofthe image capture device; and using the at least two rotational degreesof freedom on the subject mount to a desired region of interest of thesubject.

In some embodiments, the image capture device may include one of anultrasound system, an OCT system, a scanning laser ophthalmoscopesystem, a digital photography system, a film or video camera, and anobservation port.

In further embodiments, the system may further include a bite barassociated with the first structure. The bite bar may be configured toaid positioning the subject in the mount of the first structure. Thebite bar may have a translational axis and an elevation axis.

In still further embodiments, the system may further include analignment aid positioned at the intersection of the axes of the at leasttwo rotational degrees of freedom, the alignment aid including afiducial and being configured to guide placement of the subject in themount of the first structure. The fiducial may be an imaging phantom.The imaging phantom may be a ball lens with a front surface and a backsurface. The ball lens may include a layered structure on the backsurface, the layered structure including features substantially thinnerthan the imaging depth of field of the image capture device, and equalto or greater than an axial resolution of the image capture device.

In some embodiments, the ball lens may include a patterned structure onthe back surface, the patterned structure including featuressubstantially smaller than the imaging field of view of the imagecapture device, and equal to or greater than a lateral resolution of theimage capture device.

In further embodiments, the first structure may include an attachmentstructure configured to be used for mounting at least one of a bite barand an alignment fiducial. The attachment structure may include at leastone of a pair of alignment pins and a magnet. The mount for the subjectof the first structure may further include an integrated heater forwarming the subject. The integrated heater may include flow tubesembedded in the mount configured to hold or flow a warm liquid and/orgas.

In still further embodiments, the integrated heater may includeelectrically insulated electrical resistance heaters embedded in themount.

In some embodiments, the image capture device may include an alignmentfixture that is configured to physically indicate a proper position of asubject to be imaged with respect to the image capture device. Incertain embodiments, the alignment fixture may be removable.

In further embodiments, the alignment fixture of the image capturedevice and a fiducial of the mount of the first structure may intersectat the proper position for placement of the nodal point of the subjectto be imaged.

In still further embodiments, the image capture device and the subjectare configured to be rotated and/or translated with respect to oneanother to support imaging of structures not along the optical axis ofthe subject or near the nodal point of the subject.

In some embodiments, the mount of the first structure may be configuredto rotate the subject from a position aligned to image one eye to aposition aligned to image a second eye rapidly without removing thesubject from the mount.

Further embodiments provide methods for imaging an eye of an animalsubject, the method comprising adjusting a position of a nodal point ofan eye of the animal subject such that two orthogonal rotational axesintersect substantially at the nodal point of the eye of the animalsubject; and adjusting an optical axis of an observation device tosubstantially intersect the intersection of the two rotational axissubstantially at the nodal point of the subject.

In still further embodiments, the method may further include positioningthe animal subject in a mount of a first structure; and positioning anobservation device in a mount in a second structure. Positioning theanimal subject may include positioning the animal subject in the mountof the first structure using a bite bar. The bite bar may have atranslational axis and an elevation axis.

In some embodiments, the observation device may include an image capturedevice or an object configured to be peered through.

In further embodiments, the nodal point of the eye of the animal subjectmay be approximated by the approximate center of a pupil of the animalsubject.

Still further embodiments provide methods for imaging the retina of asmall animal subject, the method including positioning the small animalsubject in a mount with at least two degrees of motional freedom;mounting an image capture device on a mount with at least two additionaldegrees of freedom, the at least two additional degrees of freedom notbeing coupled to the degrees of freedom of the subject; applying acombination of rotation and translation to position a nodal point of aneye of the small animal subject at an intersection of two orthogonaldegrees of motional freedom; and aligning the image capture device suchthat an optical axis of the image capture device is substantiallyparallel to an optical axis of the subject and substantially intersectsthe intersection of the two orthogonal degrees of motional freedom ofthe subject, substantially at the nodal point of the eye of the smallanimal subject.

In some embodiments the nodal point of the eye of the small animalsubject may be approximated by the approximate center of a pupil of thesmall animal subject.

In further embodiments, the method may further include adjustingrelative positions of the small animal subject and the image capturedevice along the rotational and translational degrees of freedom toimprove the intersection of the rotational and translational axes tooptimize brightness of a retinal image.

In still further embodiments, the method may further include imagingoff-axis retinal structures by rotating the small animal subject aboutthe nodal point of the eye of the subject.

Some embodiments provide methods for imaging an eye of an animalsubject, the method including positioning the animal subject in a mountof a first structure using a bite bar; positioning an observation devicein a mount in a second structure; adjusting a position of a nodal pointof an eye of the animal subject such that two orthogonal rotational axesintersect substantially at the nodal point of the eye of the animalsubject; and adjusting an optical axis of an observation device tosubstantially intersect the intersection of the two rotational axessubstantially at the nodal point of the subject.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an Animal Imaging Mount (AIM)-RodentAlignment Stage (RAS) system in accordance with some embodiments.

FIG. 2 is a diagram illustrating an AIM-RAS system modified to include abite bar that fits to a base that is affixed to the rodent cassette inaccordance with some embodiments.

FIG. 3 is a perspective view of an imaging system, showing the locationof the nodal point at the intersection of the x, y, and z axes inaccordance with some embodiments.

FIG. 4 is a diagram illustrating placement of the nodal point in theeye, where the ocular pivot point coincides with the nodal point inaccordance with some embodiments.

FIGS. 5A through 5D are diagrams illustrating optics for mouse and ratretinal imaging, and include the anterior segment bore in accordancewith some embodiments.

FIGS. 6A and 6B are schematics of the mouse and rat eyes, whichillustrate the need for the specialized optics in accordance with someembodiments.

FIG. 7 is a diagram illustrating a mouse cassette with bite bar inaccordance with some embodiments.

FIG. 8 is a diagram illustrating a mouse cassette with bite bar,indicating the rodent chin rest for proper elevation of head inaccordance with some embodiments.

FIG. 9 is a diagram illustrating a mouse cassette with bite bar,indicating rotation compass in accordance with some embodiments.

FIG. 10 is a diagram illustrating a large rodent/rat cassette with bitebar in accordance with some embodiments.

FIG. 11 is a diagram illustrating a bite bar in accordance with someembodiments.

FIG. 12 is a diagram illustrating a bite bar in accordance with someembodiments.

FIG. 13 is a diagram illustrating a side view of a bite bar inaccordance with some embodiments.

FIG. 14 illustrates an exploded view of a bite bar in accordance withsome embodiments.

FIG. 15 is a diagram illustrating a centration fiducial, lens adapter,and phantom in accordance with some embodiments.

FIGS. 16A through 16C are diagrams illustrating optical phantoms inaccordance with some embodiments.

FIGS. 17-19 are flowcharts illustrating various methods in accordancewith some embodiments.

DETAILED DESCRIPTION

Specific exemplary embodiments of the invention now will be describedwith reference to the accompanying drawings. This invention may,however, be embodied in many different forms and should not be construedas limited to the embodiments set forth herein; rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thoseskilled in the art. The terminology used in the detailed description ofthe particular exemplary embodiments illustrated in the accompanyingdrawings is not intended to be limiting of the invention. In thedrawings, like numbers refer to like elements.

As used herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless expressly stated otherwise. Itwill be further understood that the terms “includes,” “comprises,”“including” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof. It will be understood thatwhen an element is referred to as being “connected” or “coupled” toanother element, it can be directly connected or coupled to the otherelement or intervening elements may be present. Furthermore, “connected”or “coupled” as used herein may include wirelessly connected or coupled.As used herein, the term “and/or” includes any and all combinations ofone or more of the associated listed items.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this invention belongs. It will befurther understood that terms, such as those defined in commonly useddictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andthis specification and will not be interpreted in an idealized or overlyformal sense unless expressly so defined herein.

As discussed above, preclinical imaging of small animals, for example,rodents, is important in drug development and research exploringgenetics and the early diagnosis of diseases. There is a need for ananimal mount that enables the handling of rodents, that allows anoperator to make fine adjustments to the axes of the animal eye, whichcan be thought of in terms of a coordinate system in x, y, and z, withtwo angular adjustments for the azimuthal and elevation angles. To imageproperly, the optical imaging system has to be aligned to the opticalaxis and depth of the subject eye using five degrees of freedom—twolateral orthogonal to the optical axis, one parallel to the opticalaxis, and two rotational degrees about the optical axis, for example,pitch and yaw. Cylindrical symmetry of the eye generally makes rollunnecessary to control. Furthermore, there is the additional need tohave a means of monitoring and controlling the animal's core temperatureand physiological condition. As the choice of anesthesia may compromisethe health of the animal, or at the very least result in motion that maylead to artifacts in the acquired image, the animal stage needs to beadaptable to include an optional bite bar (to reduce head motion) and anose cone for administering gaseous anesthesia if desired.

U.S. Pat. No. 7,426,904 to Zan et al., U.S. Pat. No. 7,133,713 to Zanand U.S. Pat. No. 5,320,069 to Anderson et al. discuss a need for asmall animal holder. Furthermore, Simultaneous fundus imaging andoptical coherence tomography of the mouse retina (Invest Ophthalmol. VisSci. 2007; 48 (3): 1283-1289) to Koçaoglu et al. discusses an animalstage design specifically for coupling with an OCT system, but none ofthese approaches addresses the need to be able to identify, control, androtate about the optical axis of the rodent eye in a systematic,deterministic manner. Aligning to the nodal point of the subject eye isimportant because it makes for rapid optimization of image quality andenables easy deterministic exploration of the subject eye with simple,small systematic adjustments. Without aligning to the nodal point,imaging of posterior structures of the subject eye may be verydifficult. In particular, even slight misalignments may cause seriousdegradations in image quality, particularly in imaging using OCT.

It is important to design a system that incorporates all of the elementsfor precision imaging of the ocular system of these animal models. Theserequirements include, for example, a) optics suitable for the specificanimal model as discussed in United States Patent Publication No.2009/0268161 discussed above; b) an alignment stage with an appropriatemanagement of the degrees of freedom required to aim and focus on theocular structure; c) a bite bar for positioning and restraining thesubject; and d) a methodology for rapid positioning of the subject andaligning of the optics. Additional accessories may facilitate theimaging process. A bite bar designed for the subject and the alignmentsystem facilitates accurate rapid positioning of the eye. An ocularphantom is an additional need that may be useful in mimicking thesubject for practice, system validation, and calibration of the system.A system for heating, anesthetizing, and delivering therapies to thesubject without adversely impacting imaging is desirable to complete themanagement process.

Accordingly, as will be discussed further below with respect to FIGS. 1through 19, embodiments of the present invention provide systems andmethods for imaging structures that address each of the needs discussedabove.

Some embodiments discuss image capture devices. As used herein, an“image capture device” can be any device capable of viewing or capturingan image using embodiments discussed herein. For example, an imagecapture device may include an ultrasound system, an optical coherencetomography (OCT) system, a scanning laser ophthalmoscope, a digitalphotography system, or film or video camera and the like withoutdeparting from the scope of embodiments discussed herein. As usedherein, an “image capture device” may be an observation port for a humanobserver, and may or may not include any storage, temporary or permanentof the observed or captured image. As used herein, “image capturedevice”, “image observation device” and “observation device” areinterchangeable.

Although embodiments discussed herein refer to image capture devices,embodiments are not limited to this configuration. For example,embodiments discussed herein may be used with any observation device. Asused herein, an “observation device” refers to an image capture deviceor less particularly a device that a user may peer through. Thus, asused herein an observation device is not limited to any particular imagecapture device, such as OCT or ultrasound. Although ultrasound is not anoptical system, and not subject to optical constraints, it is frequentlyimportant to correlate optical images to ultrasound images. Therefore,it remains useful to consider aligning an ultrasound system to thesubject eye as if it were optical.

Some embodiments of the present invention provide, high-throughputrodent ophthalmic imaging systems including a set of optics matched tothe ocular structure of rodents; a path length management system tomatch the focus to the interferometric condition for OCT imaging ofsubject eyes with varying focal conditions and optical path lengths;fiducial markers for guiding optimal positioning of the nodal point of asubject eye; capability to switch alignment from one eye to another eyewith a simple rotation; and/or accessories for fine-tuning position ofanimal nodal point; and/or positional recordings to guide the rapid andaccurate placement of animals.

As used herein, a “small animal” refers to an animal weighing generallyless than about 5 pounds that may be readily placed in a mount orcassette with motional degrees of freedom for adjusting the position andorientation of a nodal point of the animal eye to the optical axis of animage capture device or observation device. A small animal may be murine(rodent) or piscine (fish), but may more generally be of a class ofvertebrate or invertebrate models, or stated alternatively may be of aclass of mammals, fish, insects, reptiles, amphibians, mollusks, orbirds without loss of generality. Although embodiments of the presentinvention are discussed herein with respect to small animals and, inparticular, rodents, as the subjects, embodiments discussed herein arenot limited to small animals. The subject could be any subject capableof being imaged using systems and methods discussed herein. For example,the subject may be a rodent, a rabbit, a monkey, a dog, a sheep, a cow,a fish, a spider, a turtle, a snake, a frog, an octopus, a chicken, or abird of prey or the like without departing from the scope of the presentapplication. Animals larger than about 5 pounds could readily be mountedin structures appropriately sized.

Some embodiments discussed herein provide a mechanism for optimallyaligned high-quality images of an eye of a subject, for example, arodent eye, and increased field-of-view imaging through rotations aroundthe nodal point of the subject eye. As used herein, a “nodal point” of athin optical system refers to an abstract point in the optical systemwhere a light ray entering the nodal point appears to exit the nodalpoint in the same direction. A nodal point is an abstract ormathematical concept. Thus, in some embodiments discussed herein, thenodal point of the subject may be approximated by the approximate centerof the pupil of the subject eye.

Systems in accordance with some embodiments have the appropriate degreesof freedom to identify, align and steer around the nodal point, makingfor high-throughput imaging. As will be discussed further below withrespect to FIGS. 1 through 19, systems in accordance with someembodiments of the present invention include a mount for an imagingprobe, which can be steered toward a rotary small animal stage. Thesmall animal stage may include a cassette sized to hold the small animalsubject, and may offer fine translation along the x, y, z axes on amicro scale, and adjustment of azimuthal and elevation angles of thecassette, and may include a bite bar with additional degrees of freedomto precisely tune the position of the nodal point of the eye to thecenter of rotation of the rotary stage. In some embodiments, the systemcan be modified to include a heated mount or cassette for temperaturecontrol, a nose cone for the administration of gas anesthetics, and/oran injection guide assembly which may also be used for theadministration of eye drops. Specially designed optics and referenceposition may be modified to enable the OCT imaging of either or both ofposterior segments (e.g. retina) and anterior segment (e.g. cornea) ofthe subject eye as will be discussed further herein.

Some embodiments discussed herein provide means for aligning the imagecapture device in relation to the optical axis, the pupil, and the nodalpoint of the subject. As shown in FIG. 15, this means may be providedby, for example, calibrating the position of an aiming fiducial 510 suchthat the fiducial 510 is placed at the intersection of two axes ofrotation of the subject mount; aligning the image capture device suchthat the optical axis of the image capture device intersects the axes ofrotation of the subject mount, and that this intersection coincides withthe position of the fiducial; applying the aiming tip 700 to thesubject-appropriate lens on the image capture device and using thez-axis control of screw-drive 202 (FIG. 1) of the aiming mount, bringingthe aiming tip to the fiducial 510, locking the aiming mount such thatall degrees of freedom except for the screw-drive are fixed, and markingthe position of the screw drive; retracting the position of the imagecapture device using the screw drive, allowing space for placement ofthe subject; removing the aiming fiducial and attaching the bite bar;positioning the subject into the appropriate cassette mounted on therotation structure, and securing the subject to the bite bar; bringingthe lens of the image capture device with aiming tip back in place tothe nodal position using the screw-drive 202, referring to positionmarked when aligning to the fiducial; using the motional adjustments onthe bite bar and the subject cassette, bringing the subject eye intoposition at the aiming tip; removing the aiming tip; initiating imagecapture, such as OCT scanning; adjusting the OCT reference arm such thatthe target structure is in view; fine tuning the vertical and lateralposition of the subject eye using adjustments on the bite bar tooptimize image quality; using the rotational degrees of freedom on thesubject mount to centrate the image, making final adjustments usingmicro-adjustments on the Cartesian (x,y) controls of the animal mount;steering with the rotational degrees of freedom of the animal mount tore-center the image to off-axis regions of interest

In some embodiments, axes of the at least two rotational degrees offreedom intersect. It will be understood that the axes do notnecessarily intersect at a specific angle as the angle changes duringrotation.

As will be discussed further herein, in some embodiments of the presentinvention, the system can be modified to include accessories forintervention while imaging that can be used without moving the nodalpoint of the animal, to provide a high-throughput rodent imaging stagecoupled to a spectral domain OCT system.

In some embodiments of the present invention, high-throughput rodentimaging systems may be coupled with a fundus camera, The system mayfurther include a facility for mounting of an imaging probe, a facilityfor swapping optics (from specialized mouse optics to rat optics) and/ora capability to do anterior segment imaging (cornea).

In some embodiments of the present invention, high-throughput rodentimaging systems may be coupled with a fundus camera. The system mayfurther include a facility for mounting of an imaging probe and afacility for interchanging imaging optics, for example, from specializedmouse optics to rat optics or from posterior imaging optics to anteriorimaging optics.

In some embodiments of the present invention, the small animal imagingsystem may include a model eye phantom for mimicking the subject that isuseful for system alignment, calibration and maintenance. The model eyephantom may include optical characteristics functionally similar to thesubject eye, or may be non-optical to be used as a physical placementguide.

FIG. 1 is a perspective view of the AIM-RAS stage, containing the AnimalImaging Mount (AIM) holder for the imaging probe (showing a probe inplace), and the Rodent Alignment Stage (RAS) for manipulating the animalin accordance with some embodiments. FIG. 2 is a diagram illustrating anAIM-RAS system modified to include a bite bar that fits to a base thatis affixed to the rodent cassette in accordance with some embodiments.FIG. 3 is a perspective view of an imaging system, showing the locationof the nodal point at the intersection of the x, y, and z axes inaccordance with some embodiments. The rodent eye is placed precisely sothat any rotations in the system pivot about this point.

Some embodiments of the present invention will now be discussed withrespect to FIGS. 1 through 3. As referred to herein, elements 100-199refer to the RAS, elements 200-299 refer to the AIM, elements 300-399refer to the imaging probe, and elements 400-499 refer to the bite bar.As illustrated, element 100 illustrates the housing ‘gantry’ for themouse cassette 101. The mouse cassette 101 is a rotatable mountconfigured to receive the animal subject, and may be sized for differentclasses of subject, such as mouse, rat, and the like. Rotation of thiscassette 101 provides the equivalent motion of changing the elevationangle of the eye with respect to lens 301 of the optical deliverysystem. Angular elevation degrees marked off on the back of the housinggantry 100 enable precise angular positioning. The housing gantry 100 isconnected to a support structure 102 anchored by a pin to a rotary stage103, with angular degrees marked to indicate the azimuthal angleadjustments with reference to the nodal point in the subject eye. Insome embodiments of the present invention, systems are designed suchthat the nodal point of the subject eye is placed at the center ofrotation of the rotary stage 103.

FIG. 4 illustrates placement of the nodal point in the eye, where thenodal point is approximated by the pupil, and where rotational degreesof freedom intersect at this point, allowing the system to pivot aroundthis nodal point in accordance with some embodiments. When the nodalpoint and the pivot points coincide, the subject eye anatomy can beexplored with either of the angular adjustments indicated by thecircular arrows, i.e. the azimuthal and elevation angles.

Referring again to FIGS. 1 through 3, the combination of the cassette101 within the housing 100 affixed to the rotation stage 103 providestwo orthogonal angular degrees of freedom to facilitate alignment of theimaging optic 301 to the optical axis of the subject. The rotationalsystem is affixed to a pair of micrometer translation stages 104 and 105that provides Cartesian motion in a plane (x,z) parallel to the opticalaxis of the beam. Vertical translation is facilitated by a stage 106.The three Cartesian axes of adjustment 104, 105 and 106 supplement therotational degrees of freedom, and are redundant by design to degrees offreedom accessible with the AIM unit 200. The RAS alignment structure ismounted to a base 107, which is in turn mounted on pillars 108 toprovide a table and workspace around which other parts of the system maybe placed or fed.

The AIM system 200 is a mounting apparatus for the imaging probe 300.The imaging system may, in some embodiments, be an OCT imaging probe, avideo, digital or film fundus camera, a scanning laser ophthalmoscope orany similar system without departing from the scope of the presentinvention. The imaging system may, in some embodiments, be non-optical,and may include an ultrasound probe. For an OCT imaging system, a probe300 is mounted to a structure defined by 200 and 201. The imaging probe300 includes a lens 301 that may be any suitable optic for the subject.In some embodiments, the lens 301 is optimized for the subject. The lens301 could be one of a few specially designed optics for imaging mice orrat retina, or cornea in anterior segment OCT.

FIGS. 5A through 5D are diagrams illustrating optics for mouse and ratretinal imaging, and include the anterior segment bore in accordancewith some embodiments of the present invention. The optical designaddresses a problem of imaging through the ball lens of the rodent eyewhich is highly spherical, and lacking the power that would be found ina human eye. The optics are designed such that the field curvature ofthe imaging optics approximately matches the retinal curvature, with thepivot point placed at the center of the retinal curvature. FIGS. 6A and6B are schematics of the mouse and rat eyes, which illustrate the needfor the specialized optics in accordance with some embodiments.

Referring again to FIGS. 1 through 3, the alignment degrees of freedomfor the AIM may include three Cartesian degrees of freedom plus one ortwo rotational degrees of freedom. Motion in the plane defined by stages104 and 105 of the RAS is mediated through structure 206 of the AIM.Vertical motion is facilitated by a drive mechanism 205. The mountstructure rotates around a forward rotation point 207. When properlyaligned, a pivot point of the optics 301, the nodal point of the subjecteye, the rotation point 102 and the rotation point 207 are aligned alonga single vertical, allowing controlled rotations of subject relative tothe system about the nodal point of the subject.

The nodal point (FIG. 4) of the subject is an optical construct with aspecific definition as a point through which a ray appears to beundeviated. Experimentally, one does not precisely identify the nodalpoint in an imaged subject, but the performance of the system isconstructed such that there is a center of rotation within the subjecteye about which rays pivot, and from which rays focus onto the retina.Practically speaking, the nodal point as used herein is within orsomewhat posterior to the iris, and the iris forms an optical stopwithin the system. The optical system defined by lens 301 and theoptical imaging constructs of the subject eye may be visualized to bringa bundle of rays from the imaging source, whether a scanning system asin OCT or a video camera, to a pivot point in the vicinity of the iris,and a focal point coincident with the retina. More specifically, thefocus is surface, and in a well defined optical system the surface isconformally similar to the surface of the retina, providing maximumbrightness and resolution across the broadest field of view. Thisconformal similarity typically only occurs when the system is wellaligned, and achieving this alignment consistently is an objective ofsome embodiments of the present invention. The specific optics of lens301 are discussed in commonly assigned United States Patent PublicationNo. 2009/0268161, published on Oct. 29, 2009, entitled OPTICAL COHERENCETOMOGRAPHY (OCT) IMAGING SYSTEMS HAVING ADAPTABLE LENS SYSTEMS ANDRELATED METHODS AND COMPUTER PROGRAM PRODUCTS, the content of which ishereby incorporated herein by reference as if set forth in its entirety.

An additional fine control for propelling the lens 301 in a directionparallel to its optical axis is provided by way of a screw-drive 202. Insome embodiments, the screw has a pitch of ½″ per 20 turns (0.8 mm perturn). The screw may have an associated reference scale, and may includea quick release mechanism for returning the attached image capturedevice to a pre-selected position. A rodent eye can be from about 3.0 mmto about 10.0 mm in diameter, and a retina is approximately 1.0 mmthick, with individual layers being from about 50 μm to about 100 μm. Ascrew pitch of 800 μm per turn, or 100 μm per ⅛ turn, is well matched tothe level of precision desired in driving an optical imaging systemforward along the optical axis. More importantly, this screw pitch maybe matched to the pitch of the reference arm in an OCT system, whichwill be discussed further below.

An OCT imaging system is an interferometric device for recording aback-scattered signal intensity from a sample through an interference ofthe signal with a reference signal. OCT systems are well known in theart. OCT systems may be constructed in time domain (TD-OCT) or FourierDomain (FD-OCT) implementations. TD-OCT records a direct signatureproportional to the level of backscattering at a location in the samplethat is path-matched to the reference path. Obtaining a full depth imageinvolves scanning a reference arm across a distance that corresponds tothe range of interest within the sample. The interference is referred toas “coherence-gated,” because a signature above noise is only recordedwhen the sample and reference path lengths are equivalent to within anoptical path length equivalent to the coherence length of the source.The “coherence-gate” is made short, and the resolution fine, buy using abroadband source with a correspondingly short coherence length. Typicalsource bandwidths for retinal imaging are about 40 nm or greater, withresolutions (in air) of about 6 μm or less at a central wavelength ofabout 840 nm.

Fourier domain techniques rely on a Fourier transform relationshipbetween time and frequency domains. By sampling an interferometricsignal as a function of wavelength (frequency) instead of position(time), a spectral interferogram is collected that may be Fouriertransformed into a depth resolved spatial scattering signature. Thesubject of Fourier Domain OCT is well known in the art. FD-OCT anddiffers fundamentally from TD-OCT in that a reference arm is not scannedthrough the subject to collect the scattering signature, rather thereference arm is static, and the wavelengths are collected from therelevant depth either in parallel in a spectrometer based system(referred to as Spectral Domain OCT, SD-OCT), or serially using arapidly frequency-tuned source (Swept Source OCT, SS-OCT). The lattertwo implementations are functionally equivalent once the spectrum isacquired.

Though the reference arm is static during image acquisition, there is anoptimum position of the reference path length for a given path of thesample arm and a given subject. Proper adjustment of the reference armis critical for quality imaging. In some embodiments of the presentinvention, a method and apparatus for optimizing the reference positionin conjunction with the optics has been developed. In particular, asmentioned, the focal field of the optics is conformally similar to theshape of the retina. When the optics are aligned such that theseconformal surfaces coincide, the image field appears flat (thedifference between the focal field and the object plane is zero). Such acircumstance can occur at continuum of offset positions between the lens301 and the subject when the lens presents a telecentric field to thesubject. While such an optical design is plausible, and common in adultretinal imaging, the lens may not be strictly telecentric. Regardless,for any particular alignment of the optics to the subject, there is anoptimum position of the reference arm such that the interferometric pathlength matching position is appropriately correlated to the focalconditions of the optics.

In some embodiments, a particular signature of appropriate alignment ofthe optics is a flattened image of the retina. However, the focal imageis only apparent because of coordination with the path length matchingcondition. In fact, an image derived from the interferometry can bevisible with improper focus, but the converse is not true. The problemthen becomes one of co-optimization of focus and path length matchingover a broad range of subjects and optics. Some embodiments of thepresent invention address this problem.

When the focal conditions are not perfectly met, but are close, it willgenerally be possible to find a path length matching condition throughmodification of the reference arm length such that a coherently derivedimage is visible. Some embodiments may simplify the optimization processby providing a coordinated path length adjustment process. When an OCTimaging condition is achieved, though perhaps not optimized, the pathlength of the sample arm, that may under some optical design conditionsimpact the focal plane, may be adjusted in a manner coordinated with thereference arm to optimize the focal conditions while maintaining theappropriate path matching condition. Telecentric scanning optics for anemmotropic subject will image correctly independently of the distancebetween the imaging lens and the cornea. This condition is not met ingeneral, in some specific instances the imaging lens has significantoptical power, and in such a case the back focal plane is stronglyinfluenced by the distance between the lens and the cornea. In such ageneral condition, the back focal plane may be deeper than, or shallowerthan the retina. The result will be an image that causes the retina tobe curved—the center will appear deeper in the former condition, andshallower in the latter. Changing the sample distance will in such acircumstance necessitate a change in the reference arm length in orderto maintain interferometric path matching. In some embodiments of thepresent invention, the imaging lens may be moved relative to thesample—thus changing the sample arm length—using the screw drive 202.Screw drive 202 is designed specifically to correlate to the referencearm drive—in some embodiments a 1:1 drive ratio, such that the samplearm length and the reference arm are driven in unison, or in a mannerprescribed by a relationship between an optical path length to thesample position and a change in working distance. Details of thismechanism are discussed in commonly assigned United States PatentPublication No. 2009/0268161, published on Oct. 29, 2009, which has beenincorporated by reference above. The imaging result as the relativesample position—and reference arm length—are adjusted is that theapparent curvature of the image is modified. The image may be drivenfrom an upward curvature, through a flattened image, to a downwardcurvature, according to the optics. The correct optical condition isdirectly identified as that which optimizes the focal condition, and theimage appears flat.

To complete the facilitation of optical alignment, some embodiments ofthe present invention provide for a specifically designed bite bar. Bitebars are used to steady an animal subject for imaging. The bite bar 400(FIG. 2) in accordance with some embodiments provides additionalfunctionality to facilitate localization of the nodal point (FIG. 4) ofthe subject eye with the center of rotation of the alignment system, asdefined be the intersection of the center of rotation of the animalcassette 101, and the rotation of the cassette housing about the pin inthe mounting plate 102, subject to the alignment conditions definedabove.

Various embodiments of bite bars according to embodiments of the presentinvention are illustrated in FIGS. 7 through 14. FIG. 7 is a diagramillustrating a mouse cassette with bite bar in accordance with someembodiments. FIG. 8 is a diagram illustrating a mouse cassette with bitebar, indicating the rodent chin rest for proper elevation of head inaccordance with some embodiments of the present invention. FIG. 9 is adiagram illustrating a mouse cassette with bite bar, indicating rotationcompass in accordance with some embodiments of the present invention.FIG. 10 is a diagram illustrating a larger rodent/rat cassette with bitebar in accordance with some embodiments of the present invention. FIG.11 is a diagram illustrating an assemble view of a bite bar inaccordance with some embodiments of the present invention. FIG. 12 is adiagram illustrating a bite bar having magnetic pin placements inaccordance with some embodiments of the present invention. FIG. 13 is adiagram illustrating a side view of a bite bar in accordance with someembodiments of the present invention. FIG. 14 is an exploded view of abite bar in accordance with some embodiments of the present invention.

Referring now to FIGS. 7 through 14, the bite bar 400 secures the snoutof the subject animal with a bit 420, and securing strap 410. Thepressure of the securing strap 410 is controlled by spring reliefs 430.The bite assembly 401 is driven laterally by lateral screw 440, and maybe raised and lowered by elevator 450. The bite bar 400 further includesan ease of use feature that is attached to and removed from the cassette101 as it is secured by pin placement 405 and held magnetically 406.

Furthermore, it is generally desirable to be able to image either theright or the left eye, and once alignment is achieved in one to be ableto switch to the other with a minimum realignment. In some embodiments,flipping from one eye to the other is simplified by the symmetry of thegeometry. The cassette housing may be rotated quickly from right toleft, and with the bite bar the left eye moved into the final correctlater position with the lateral drive screw 403, without necessitatingany major adjustment in path length positions, focal positions, orheights.

Systems in accordance with some embodiments of the present inventionprovide an open, flexible geometry that facilitates the addition ofother tools useful in alignment, imaging, therapy, or animal management.Some embodiments of the present invention an integrated heater forwarming the subject in the mount/animal cassette 101. For example, insome embodiments, the animal cassette 101 (FIG. 1) may include radiatortubes aligned in the bottom of the cylindrical place where the subjectmay be placed. Warm water/gas may flow through the tubes to provide aninsulated electrical heater. The animal cassette 101 may be designedwith radiator tubes molded directly into the boy of the cassette, suchthat warm water/gas may be run directly to keep the cassette warm. Thetemperature of the subject may impact the subject physiologically. Forexample, if the subject, for example, a rodent, is cold, the rodent'seyes may cloud over causing the image to be distorted or the rodent todie. Providing a heated cassette 101 may not only create a morecomfortable environment for the subject, but may also help to decreaseor possibly avoid these physiological effects. In alternativeembodiments, a heating blanket that may be a warm water blanket or anelectric blanket may be used.

In some embodiments of the present invention, a fiducial indicator 510(FIG. 15) to provide evidence of the center of rotation of the systemmay be provided. Referring to FIG. 15, the system may include aprecision mounted mechanical fiducial assembly 500 or laser pointer, orcrosshair calibrated to the center of rotation to facilitate animalplacement. In some embodiments, the fiducial assembly 500 may be mountedto the rotation plate 102 such that the fiducial center is located atthe center of the axis of rotation. The fiducial assembly 500 includes acentration fiducial 510. The centration fiducial 510 may, but notnecessarily, be an optical phantom 800 (FIGS. 16A-16C) that has lensingattributes that are representative of the subject eye, and may be imagedby the optical system to verify the system set up and performance.Furthermore, in order to increase the likelihood of proper orientationof the scanning head 300, a lens adapter 700 may be attached to theimaging lens 301. The lens adapter 700 is designed to come intoimmediate contact with the fiducial 510, at which point the opticaldistances are optimized.

Referring now to FIG. 16, an optical phantom 800 may include a lens 810that mimics the optical properties of the subject. For a mouse, the lensmay be a ball lens with a diameter of from about 2.0 mm to about 4.0 mm.At the back of the lens, a structure 820 to mimic a retina is deployed.The structure may be a layered structure from about 250 μm to about 1500μm thick, with layers ranging in thickness from about 20 μm to 200 μm.Such layers can be created using cast polymers, or layers of translucenttape. The layers provide a context for visualizing axial resolution andimaging depth. Lateral features 830 may be embedded between the lens andthe layered structure or between one or more layers. The lateralstructures may be loosely woven, with feature diameters ranging betweenabout 5.0 μm and about 500 μm. Such structures may be created by a loosefabric of threads, or may be more precisely created through alithographic process without departing from the scope of the presentinvention.

Some embodiments of the present invention may provide access totherapeutic ports or alternative diagnostics. For example, the use of asyringe to inject a chemical compound, or to guide a laser forphotodynamic therapy, or a transducer for electrical or ultrasoundmeasurements. The architecture of systems according to some embodimentsof the present invention is designed to include the placement of suchancillary features that do not interfere with the optical imagingsystem, and in fact allow imaging during the course of therapy.

Small animal imaging systems in accordance with some embodiments of thepresent invention are designed to provide for optimally alignedhigh-quality images of a rodent eye, to provide for larger field of view(FOV) through rotations around the nodal point of the rodent eye. Analignment system has been created with the appropriate degrees offreedom to identify, align and steer around the nodal point of thesubject eye. The optics appropriate for imaging the differentialstructure of the rodent eye, have been designed to work with a referencearm assembly in the OCT system. The mouse cassette can be modified toinclude a heating pad, a nose cone for gas anesthesia, and a bite barfor anchoring the rodent head in the optimal position to allow formanipulations with needles or droppers. Mouse and rat eye model phantomshave also been created to aid in system calibration and alignment.

Various methods for imaging an eye of an animal subject will now bediscussed with respect to the flowcharts of FIGS. 17 through 18.Referring first to FIG. 17, operations begin at block 1740 by adjustinga position of a nodal point of an eye of the animal subject such thattwo orthogonal rotational axes intersect substantially at the nodalpoint of the eye of the animal subject. An optical axis of anobservation device is adjusted to substantially intersect theintersection of the two rotational axis substantially at the nodal pointof the subject (block 1760).

Referring now to FIG. 18, operations begin at block 1820 by positioningthe animal subject in a mount of a first structure. The observationdevice is positioned in a mount in a second structure (block 1830). Insome embodiments, positioning the animal subject includes positioningthe animal subject in the mount of the first structure using a bite bar.The bite bar may have a translational axis and an elevation axis. Theobservation device may be an image capture device or an objectconfigured to be peered through without departing from the scope of thepresent application.

A position of a nodal point of an eye of the animal subject may beadjusted such that two orthogonal rotational axes intersectsubstantially at the nodal point of the eye of the animal subject (block1840). An optical axis of an observation device is adjusted tosubstantially intersect the intersection of the two rotational axissubstantially at the nodal point of the subject (block 1860). In certainembodiments, the nodal point of the eye of the animal subject may beapproximated by a pupil of the animal subject.

Referring now to FIG. 19, operations begin at block 1923 by positioningthe small animal subject in a mount with at least two degrees ofmotional freedom. An image capture device may be mounted on a mount withat least two additional degrees of freedom, the at least two additionaldegrees of freedom not being coupled to the degrees of freedom of thesubject (block 1933). A combination of rotation and translation may beapplied to position a nodal point of an eye of the small animal subjectat an intersection of two orthogonal degrees of motional freedom (block1943). In some embodiments, the nodal point of the eye of the smallanimal subject may be approximated by a pupil of the small animalsubject. The image capture device may be aligned such that an opticalaxis of the image capture device is substantially parallel to an opticalaxis of the subject and substantially intersects the intersection of thetwo orthogonal degrees of motional freedom of the subject, substantiallyat the nodal point of the eye of the small animal subject (block 1963).

As discussed briefly above with respect to FIGS. 1 through 19,high-throughput small animal imaging systems in accordance with someembodiments of the present invention include an optical alignment systemthat decouples lateral and rotational degrees of freedom for managingimaging of the particular ocular geometries of small animals, such asrodents and small monkeys. Systems in accordance with some embodimentsof the present invention include a stage with an imaging mount capableof translating an imaging probe about multiple degrees of freedom arounda small animal stage equipped with an animal-specific rotationalcassette having translational and rotational degrees of freedom tomanipulate the animal head. The manipulation of the animal eye is doneabout an optical nodal point, and allows the operator to opticallyexplore the rodent retina with precision using systematicmicro-manipulations. Systems in accordance with some embodiments of thepresent invention provide for rapid and precise placement of both eyes,with shifts from left and right by way of a quick lateral shift. Theassembly can be modified to image both rodent posterior (retina) andanterior segment with specially-designed optical bores and coordinationof reference arm optical path lengths for optical coherence tomographyimaging. The system may include a heating pad to keep the animaltemperature within a range. The assembly may be modified also to includeneedle-guided apparatus or other apparatus that needs access to therodent eye during imaging without moving the animal from the optimalimaging position. The small animal stage may include a bite bar toreduce the likelihood animal head motion during such procedures, and anose cone for administering gaseous anesthesia.

In the drawings and specification, there have been disclosed exemplaryembodiments of the invention emphasizing the utility for imaging animalsubjects. However, many other subjects may benefit from the generalembodiments of this invention. Any subject that possess a nodal point,and particularly subjects for which, like the eye, it is desirable toimage through an optical stop to features posterior to the stop maybenefit from the application of embodiments of this invention. Forexample, it may be desirable to image phantom eye models withembodiments of this invention.

In the drawings and specification, there have been disclosed exemplaryembodiments of the invention. However, many variations and modificationscan be made to these embodiments without substantially departing fromthe principles of the present invention. Accordingly, although specificterms are used, they are used in a generic and descriptive sense onlyand not for purposes of limitation, the scope of the invention beingdefined by the following claims.

1. A system for imaging structures of a subject, the subject having anoptical axis, a pupil, and a nodal point, the system comprising: animage capture device; a first structure including a mount for thesubject to be imaged by the image capture device, the first structureproviding at least two rotational degrees of freedom; a second structureincluding a mount for the image capture device, the second structureproviding at least two translational degrees of freedom; and a means foraligning the image capture device in relation to the optical axis, thepupil, and the nodal point of the subject.
 2. The system of claim 1,wherein axes of the at least two rotational degrees of freedom of thefirst structure intersect.
 3. The system of claim 2, further comprisingan alignment aid positioned at the intersection of the axes of the atleast two rotational degrees of freedom, the alignment aid including afiducial and being configured to guide placement of the subject in themount of the first structure.
 4. The system of claim 3, wherein thefiducial comprises an imaging phantom.
 5. The system of claim 4, whereinthe imaging phantom comprises a ball lens with a front surface and aback surface.
 6. The system of claim 5, wherein the ball lens comprisesa layered structure on the back surface, the layered structure includingfeatures substantially thinner than the imaging depth of field of theimage capture device, and equal to or greater than an axial resolutionof the image capture device.
 7. The system of claim 5, wherein the balllens comprises a patterned structure on the back surface, the patternedstructure including features substantially smaller than the imagingfield of view of the image capture device, and equal to or greater thana lateral resolution of the image capture device.
 8. The system of claim2, wherein an optical axis of the image capture device mounted on thesecond structure is aligned to intersect the intersecting axes of the atleast two rotational degrees of freedom of first structure.
 9. Thesystem of claim 8, wherein the mount for the subject in the firststructure is configured such that the optical axis of the subject isaligned to within about 5.0 degrees of the optical axis of the imagecapture device mounted to the second structure when the subject ispositioned in the mount of the first structure.
 10. The system of claim9, wherein the subject is aligned to within from about 0.0 degrees toabout and 45.0 degrees.
 11. The system of claim 2, wherein the mount ofthe first structure is configured such that the axes of the tworotational degrees of freedom intersect at the nodal point of thesubject when the subject is positioned in the mount of the firststructure.
 12. The system of claim 11, wherein the nodal point of thesubject is approximated by an approximate center of a pupil of thesubject.
 13. The system of claim 11, wherein an optical axis of theimage capture device of the second structure is rotated about the nodalpoint of the subject of the first structure such that an angle betweenthe optical axis of the image capture device and the optical axis of thesubject sweeps through a cone of at least about 15.0 degrees in at leasttwo non-co-planar directions.
 14. The system of claim 11, wherein anoptical axis of the image capture device of the second structure isrotated about the nodal point of the subject of the first structure suchthat an angle between the optical axis of the image capture device andthe optical axis of the subject sweeps through a cone of at least about30.0 degrees in at least two non-co-planar directions.
 15. The system ofclaim 2, wherein the at least two rotational degrees of freedom of thefirst structure include a rotation about a first axis substantiallyparallel to a first axis of symmetry of the subject and a rotation aboutan orthogonal second axis substantially parallel to a second axis ofsymmetry of the subject.
 16. The system of claim 15: wherein the subjectis a small animal; and wherein the first axis of symmetry of the smallanimal is an axis of the body that separates a right side of the smallanimal from a left side of the small animal and a right eye of the smallanimal from a left eye of the small animal.
 17. The system of claim 16,wherein the second axis of symmetry of the small animal is an axisorthogonal to the axis of the body located such that the pupil of atleast one eye of the small animal lies in the plane.
 18. The system ofclaim 17, wherein the small animal comprises one of a rodent, a rabbit,a monkey, a dog, a sheep, a cow, a fish, a spider, a turtle, a snake, afrog, an octopus, a chicken, or a bird of prey.
 19. The system of claim17, wherein the small animal comprises one of a mammal, a fish, a bird,a reptile, an amphibian, an insect, or a mollusk.
 20. The system ofclaim 1, wherein the subject comprises an animal.
 21. The system ofclaim 20, wherein the animal is a vertebrate or an invertebrate animal.22. The system of claim 1, wherein the means for aligning comprises:identifying an intersection of two axes of rotation of the subjectmount; aligning the image capture device such that an optical axis ofthe image capture device intersects the axes of rotation of the subjectmount; positioning the subject such that the nodal point of the subjecteye is located at the intersection of these two axes of rotation and animaging axis of the image capture device; and using the at least tworotational degrees of freedom on the subject mount to a desired regionof interest of the subject.
 23. The system of claim 1, wherein the imagecapture device comprises one of ultrasound system, an OCT system, ascanning laser ophthalmoscope system, a digital photography system, afilm or video camera, and an observation port.
 24. The system of claim1, further comprising a bite bar associated with the first structure,the bite bar being configured to aid positioning the subject in themount of the first structure.
 25. The system of claim 24, wherein thebite bar has a translational axis and an elevation axis.
 26. The systemof claim 1, wherein the first structure comprises an attachmentstructure configured to be used for mounting at least one of a bite barand an alignment fiducial.
 27. The system of claim 26, wherein theattachment structure comprises at least one of a pair of alignment pinsand a magnet.
 28. The system of claim 26, wherein the mount for thesubject of the first structure further comprises an integrated heaterfor warming the subject.
 29. The system of claim 28, wherein theintegrated heater comprises flow tubes embedded in the mount configuredto hold or flow a warm liquid and/or gas.
 30. The system of claim 28,wherein the integrated heater comprises electrically insulatedelectrical resistance heaters embedded in the mount.
 31. The system ofclaim 1, where the image capture device comprises an alignment fixturethat is configured to physically indicate a proper position of a subjectto be imaged with respect to the image capture device.
 32. The system ofclaim 31, wherein the alignment fixture is removable.
 33. The system ofclaim 31, wherein the alignment fixture of the image capture device anda fiducial of the mount of the first structure intersect at the properposition for placement of the nodal point of the subject to be imaged.34. The system of claim 1, wherein the image capture device and thesubject are configured to be rotated and/or translated with respect toone another to support imaging of structures not along the optical axisof the subject or near the nodal point of the subject.
 35. The system ofclaim 1, wherein the mount of the first structure is configured torotate the subject from a position aligned to image one eye to aposition aligned to image a second eye rapidly without removing thesubject from the mount.
 36. A method for imaging the retina of a smallanimal subject, the method comprising: positioning the small animalsubject in a mount with at least two degrees of motional freedom;mounting an image capture device on a mount with at least two additionaldegrees of freedom, the at least two additional degrees of freedom notbeing coupled to the degrees of freedom of the subject; applying acombination of rotation and translation to position a nodal point of aneye of the small animal subject at an intersection of two orthogonaldegrees of motional freedom; and aligning the image capture device suchthat an optical axis of the image capture device is substantiallyparallel to an optical axis of the subject and substantially intersectsthe intersection of the two orthogonal degrees of motional freedom ofthe subject, substantially at the nodal point of the eye of the smallanimal subject.
 37. The method of claim 36, wherein the nodal point ofthe eye of the small animal subject is approximated by an approximatecenter of a pupil of the small animal subject.
 38. The method of claim36 further comprising: adjusting relative positions of the small animalsubject and the image capture device along the rotational andtranslational degrees of freedom to improve the intersection of therotational and translational axes to optimize brightness of a retinalimage.
 39. A method for imaging an eye of an animal subject, the methodcomprising: positioning the animal subject in a mount of a firststructure using a bite bar; positioning an observation device in a mountin a second structure; adjusting a position of a nodal point of an eyeof the animal subject such that two orthogonal rotational axes intersectsubstantially at the nodal point of the eye of the animal subject; andadjusting an optical axis of an observation device to substantiallyintersect the intersection of the two rotational axes substantially atthe nodal point of the subject.